In many conventional internal combustion engines the pistons are connected to a crankshaft through a connecting rod. The connecting rod pivots about a point where it is attached to the piston at the top of the connecting rod, which moves mostly vertically with piston. The lower end of the connecting rod, however, reciprocates circularly with the crankshaft connecting rod journal. This conventional arrangement is used in may common engines.
One of the most common engines in automotive applications is the inline four cylinder engine. The inline four cylinder engine has been around and in production since the early 1900's but has suffered from various inherent design flaws which have limited the maximum displacement of the engine design to around 2.5 liters. The normal inline four cylinder configuration has very little rocking which typically results in smooth middle rpm range. However, these engines are known to produce a secondary imbalance, which is undesirable for high rpm. This secondary imbalance is largely caused by the fact that the pistons move together in pairs, offset in timing by 180 degrees. The two pistons moving upward toward top dead center travel a greater distance from the mid stroke position than the two pistons moving downward from the mid stroke position toward bottom dead center. This difference in travel over the same amount of time causes the secondary imbalance and creates two upward out of balance pulses per revolution. Rotational vibration on the X axis, which is often felt during idling, tend to be large because, in addition to the non-overlapping power stroke inherent in engines with 4 or fewer cylinders, the height imbalance from the connecting rods' center of gravity swinging left and right is amplified due to there being two connecting rods moving together.
For inline four cylinder engines there are three types of crankshaft designs that attempt to mitigate or dampen these undesirable forces. These designs include crankshafts with no counter weights, crankshafts that are fully counter-weighted, and crankshafts that are semi-counter or half-counter weighted. Crankshafts without counter weights were used on engines up to the mid-1930s for automobiles, but are still to be found in agricultural use (with the known imbalance problems). Without counter weight an inline four cylinder engine crank is balanced for primary forces, primary and secondary couples, but not for secondary forces. Secondary forces cannot be balanced on the crankshaft, and are address by using two contra-rotating balance shafts running at twice engine speed. These balance shafts are typically only provided on premium quality cars that demand very smooth running, or on large engines in excess of 2.4 L where the level of secondary vibration becomes obtrusive. The primary couples bend the crank to an S shape with the deflection increasing with rpm. Without counter weights this deflection causes fatigue and main bearing failures when the deflection exceeds the bearing clearance, resulting in rubs (i.e. breaches of the lubricant layer). These failures have resulted in a public perception that high rpm operation is bad for the inline four cylinder engine that lingers to this day. This has been address in some crankshafts which have two counter weights on each crank throw while other crankshafts have one counter weight on each crank throw, which are on each end of the crankshaft and on both sides of the center. The counter weights balance each other completely for primary forces and couples and have no secondary forces/couple. Many prior art engine designs have been created in an attempt to overcome the secondary imbalance forces but all are merely a solution which allows the engine vibration to not be felt by the operator while the forces are still experienced in the engine. These forces eventually overcome the lubrication film gap and cause the engine to fail.
Thus, the four cylinder inline engine design suffers from two major inherent design flaws, one being the fact that connecting rods swing in pairs from side to side and the second is the pair of pistons traveling at different speeds causing the secondary imbalance problem. Both of these conditions cause severe loads on the crankshaft and crankshaft bearings causing severe engine failures. Therefore, a need exists to overcome the problems with the prior art as discussed above.